In order to produce small-sized, thin, and high-density electronic instruments, a multilayer printed wiring board has been frequently used. By providing a layer including high-dielectric constant materials on the inner layer or surface layer of such a multilayer printed wiring board to improve the package density, it becomes possible to cope with demand for production of smaller-sized, thinner, and higher-density electronic instruments.
Conventionally, a ceramic sintered body obtained by molding ceramic powders and then sintering the resultant has been used as a high-dielectric constant material. Thus, the size and shape of the material has been restricted by a molding method. In addition, since a sintered body is very hard and fragile, it has been difficult to process the sintered body freely, and thus it has been extremely difficult to obtain any given shape or a complicated shape.
In this regard, a composite dielectric material formed by dispersing an inorganic filler with a high dielectric constant in a resin has drawn attention due to its high processability. For example, a perovskite type composite oxide is known as such an inorganic filler with a high dielectric constant used herein (see, for example, Patent Citation 1). However, the perovskite type composite oxide has a problem in that the specific surface area changes over time and the dielectric characteristics are deteriorated. In addition, it has another problem in that when it is brought into contact with water, A-site metals such as Ba, Ca, Sr, and Mg in the structure are eluted, and thus, peeling of the interface between the resin and the inorganic filler or deterioration in insulation due to ion migration occurs.
Meanwhile, as described in Patent Citations 2 to 6, it is known that an inorganic filler with a high dielectric constant, such as barium titanate, is surface-treated with a coupling agent for the purpose of improving dispersibility in a resin.    Patent Citation 1: Pamphlet of International Publication WO 2005/093763    Patent Citation 2: Japanese Patent Laid-Open No. 2003-49092    Patent Citation 3: Japanese Patent Laid-Open No. 2004-253219    Patent Citation 4: Japanese Patent Laid-Open No. 2005-2281    Patent Citation 5: Japanese Patent Laid-Open No. 2005-8665    Patent Citation 6: Japanese Patent Laid-Open No. 2005-15652